从Doctrine2中的集合中删除元素

Question

I have a Command entity which has a n:m relationship with Alias. This is a piece of code of the Command class:

class Command
{

    ...

    /**
     * @ORM\ManyToMany(targetEntity="Alias", inversedBy="alias_command", cascade={"persist", "remove"})
     * @ORM\JoinTable(name="command_has_alias",
     *      joinColumns={@ORM\JoinColumn(name="command_id", referencedColumnName="id")},
     *      inverseJoinColumns={@ORM\JoinColumn(name="alias_id", referencedColumnName="id")}
     * )
     */
    protected $command_alias;

    public function __construct()
    {
        $this->command_alias = new ArrayCollection();
    }

    ...

    /**
     * Add alias to command.
     * @param Alias $alias
     */
    public function addCommandAlias(Alias $alias)
    {
        $this->command_alias[] = $alias;
    }

    /**
     * Get alias from command.
     * @return Doctrine\Common\Collections\Collection
     */
    public function getCommandAlias()
    {
        return $this->command_alias;
    }

    /**
     * Remove alias from command.
     * @param Alias $alias
     */
    public function removeCommandAlias(Alias $alias)
    {
        $this->command_alias->removeElement($alias);
        return $this;
    }
}

I want to delete an element from the collection (association in n:m intermediary table) but what I have is the ID of the Alias. I read Doctrine docs around Removing associations but is not clear to me how to delete the element from the collection. I don't know if remove by key is the path to follow here or if I can do something in my entity to get this easy anyway I will not remove the Command and either the Alias I just want to remove the relation between them. Any advice?

Answer 1

This should be pretty straigthforward. If all you need to do is remove relation between an alias and a command, while having alias ID, add following method to Command:

public function removeAliasById($aliasId)
{
    foreach ($this->command_alias as $alias) {
        if ($alias->getId() == $aliasId) {
            $this->command_alias->removeElement($alias);
            return;
        }
    }
}

When you have that, removing alias from command by id is:

$command->removeAliasById($aliasId);
$entityManager->persist($command);
$entityManager->flush();